Ethylene vinyl alcohol copolymer is a well know polymer that can be produced by a two-step process of polymerization and saponification as follows:

As a result of this two-step process of polymerization and saponification, polymer can be produced in pellet form. However, the production of the pellet is not uniform in size. When attempting to utilize the EVOH pellets of the prior art, there is a problem of poor delivery efficiency in feeding the extruder used to produce films of the EVOH. This poor efficiency and instability in feeding the extruder can be observed in an unstable operating electric current in the motor turning the extruder screw; and blow holes or translucent irregularities as evident by visual or instrument inspection of the final product. Because ethylene vinyl alcohol copolymer is a semi-crystalline random copolymer of ethylene and vinyl alcohol and has high transparency, it is widely and most commonly used as packaging structures for perishable foods. However, one of the most important properties required for this use is its superior barrier properties to oxygen. Ethylene vinyl alcohol copolymer films that have translucent irregularities and/or low oxygen barrier properties caused by blow holes in the film are therefore not acceptable films.
As a result of observing these phenomena, the present inventors realized that production of inferior ethylene vinyl alcohol copolymer films was attributable to bridging occurring in the mass of pellets being introduced into, and/or conveyed by the extruder screw. Bridging among the mass of individual pellets means that there is a non-uniform, or even absence, of conveying pellets immediately downstream of the bridging phenomena. Bridging is also one of the reasons that unstable operating electric currents are observed in the electric motor turning the extruder screw. Bridging among the mass of pellets also accounts for the occurrence of blow holes in the final product as the result of unequal metering and conveying of the mass of pellets through the extruder.
Prior art attempts at solving bridging problems were directed at mixing pellets of circular or elliptical cross-section pellets (A1) with pellets of cylindrical shape (A2) in a specified ratio of pellets of A1:A2 being from 99:1 to 20:80 as described in Taiwanese published patent application TW 201531489A. The problem with such a solution required two production lines to form pellets of two distinctive shapes, plus the additional step of mixing the pellets of two different shapes in a specific ratio. Another attempt at extrusion of EVOH copolymer resin can be found in Chinese patent CN 1262595C in which an EVOH copolymer resin was fed into an extruder and while maintain the temperature of the melting resin at 70 to 170° C., and adjusting the amount of water by supplying or removing water in the extruder. Alkali metal salt or alkali earth metal salt was added to the extruder which was the reason that the water content was controlled. However, ethylene vinyl alcohol copolymer is a hydrophilic material, so the ethylene vinyl alcohol copolymer resin must be dry prior to extrusion processing. Not only is this prior process costly, but the additive and water content in the extruder might reduce the heat resistance and other properties of the final product.
Thus, there currently does not exist any known manner of improving the stability of delivery of EVOH copolymer pellets to an extruder in order to produce high quality film without blowholes, translucent irregularities and/or poor oxygen barrier properties.